THE PLATINUM METALS 371 



All the platinum metals, like those of the iron group, are grey, with 

 a comparatively feeble metallic lustre, and are very infusible. In this 

 respect they stand in the same order as the metals of the iron series ; 

 nickel is more fusible and whiter than cobalt and iron, so also palla- 

 dium is whiter and more fusible than rhodium and ruthenium, and 

 platinum is comparatively more fusible and whiter than iridium or 

 osmium. The saline compounds of these metals are red or yellow, like 

 those of the majority of the metals of the iron series, and like the 

 latter, the different forms of oxidation present different colours. More- 

 @yer, certain complex compounds of the platinum metals, like certain 

 complex compounds of the iron series, either have particular character- 

 istic tints or else are colourless. 



The platinum metals are found in nature associated together in 

 alluvial deposits in a few localities, from which they are washed, 

 owing to their very considerable density, which enables a stream of 

 water to wash away the sand and clay with which they are mixed. 

 Platinum deposits are chiefly known in the Urals, and also in Brazil 

 and a few other localities. The platinum ore washed from these 

 alluvial deposits presents the appearance of more or less coarse grains, 

 and sometimes, as it were, of semi-fused nuggets. 2 



All the platinum metals give compounds with the halogens, and th 

 highest haloid type of combination for all is RX 4 . For the majority 

 of the platinum metals this type is exceedingly unstable ; the lower 

 compounds corresponding to the type RX 2 , which are formed by th^ 

 separation of X 2 , are more stable. In the type RX 8 the platinum 

 metals form more stable salts, which offer no little resemblance to 



from platinum, of such a double salt as PtCl 2 ,2KCl, is accompanied by a comparatively 

 small evolution of heat (see Chapter XXI., Note 40), for instance, Pt+Cl 2 -f-2KCl-f Aq 

 only evolves about 88,000 calories (hence the reaction, Pt-f-Cl 2 +Aq,. will evidently 

 disengage still less, because PtCl 2 + 2KCl evolves a certain amount of heat), whilst on 

 the other hand, Fe + Cl 2 +Aq gives 100,000 calories, and even the reaction with copper 

 (for the formation of the double salt) evolves 68,000 calories. 



2 The largest amount of platinum is extracted in the Ura^s, about five tons annually. 

 A certain amount of gold is extracted from the washed platinum by means of mercury, 

 which does not dissolve the platinum metals but dissolves the gold accompanying the 

 platinum in its ores. Moreover, the ores of platinum always contain metals of the iron 

 series associated with them. The washed and mechanically sorted ore in the majority 

 of cases contains about 70 to 80 p.c. of platinum, about 5 to 8 p.c. of indium, and a some- 

 what smaller quantity of osmium. The other platinum metals palladium, rhodium, and 

 ruthenium occur in smaller proportions than the three above named. Sometimes grains 

 of almost pure osmium-iridium, containing only a small quantity of other metals, are 

 found in platinum, ores. This osmium-iridium may be easily separated from the other 

 platinum metals, owing to its being nearly insoluble in aqua regia, by which the latter 

 are easily dissolved. There are grains of platinum which are magnetic. The grains of 

 osmium-iridium are very hard and malleable, and are therefore used for certain pur- 

 poses, for instance, for the tips of gold pens. 



